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Old 02-07-2014, 05:39 AM   #1
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Larisa Bulavina
Singapore, SG
Join Date: Jun 2011
Posts: 60
UNUSUAL RIG: need help!

Hey guys,

I need to animate chromatin, i.e. how DNA looks like inside the nucleus of non-dividing cell. The illustration for it is here:

So, it is not just DNA, but a complex of DNA with proteins that has a particular structure, which is still debatable (solenoid or zigzag form, etc.). Hence, I chose slightly modified “pebbles” paint fx brush, which suggests that complex undefined structure.
All molecules should be in constant Brownian motion, which I assigned on 2 different levels: turbulence on paint fx stroke, as well as a turbulence field on the curve; the curve was converted to a soft body (with the original as goal).
Test-animation can be seen here:

If it were simply a “clump” that has to move randomly, my task would be finished.
However, there are “loops” of chromatin, where the actual transcription of mRNA takes place. These loops move non- randomly: they leave their “clump” (called chromosome territory) to loop out into the interchromatin space, where transcription enzymes are situated. Here lies the actual problem. If the curve was not so “clumpy” and complex, I could make joints, IK and cluster controls. As a matter of fact, I tried that, but it does not work nicely on this complex and highly looped curve.
Somehow I should be able to “pull out” the loop during the animation, but without stretching the curve (this makes paint fx stroke look stretched and “diluted”). So, I cannot just pull and keyframe single vertices.
What else can I do?
Old 02-07-2014, 05:26 PM   #2
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Michele Bousquet
Senior Editor
CG Freelancer Magazine
New Orleans, USA
Join Date: Dec 2006
Posts: 36
Which software are you using? Would a Spline IK type of solution work for this?
Michele Bousquet
CG Freelancer Magazine
Old 02-07-2014, 08:50 PM   #3
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One idea that came to my mind is that you could cheat in postproduction. I mean, first render that whole DNA chain with turbulence and zoom to that single loop and then animate your single loop manually, render it and mix these two animations in After Effects or something.
But if you can't cheat, then:
I guess you use Maya. I have no experience with paint effects but I assume that this is a set of ordinary meshes. You can for example duplicate one DNA loop twice, lets call them MyLoop, and ManualLoop so that you have 3 copies of the same loop. The third one which is still a paint effect can be called PELoop. Now create a blend shape node on MyLoop with two targets: ManualLoop and PELoop and with world (not local!!!) origin checked in the Create -blendshape -options. PELoop is animated by turbulence field and should be invisible, ManualLoop is animated by your manual controls for transformation and rotation and also should be hidden. MyLoop is the only copy that is actually visible in the scene. The moment when the loop separates from the rest of the chain is the moment when you blend between the targets of your blend shape node.
As I said, I never worked with paint effects and can't say if making a such blendshape is possible.
And maybe you need only one target for your loop and just turn off the envelope of the blendshape node when you want to animate it manually.

Last edited by numnah13 : 02-07-2014 at 09:03 PM.
Old 02-08-2014, 11:52 AM   #4
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Larisa Bulavina
Singapore, SG
Join Date: Jun 2011
Posts: 60
Thanks, guys! It's Maya, which I, of course, forgot to mention.

Numnah13, it´ s a nice advice, thank you!
I'll go for it, if the paint FX modifiers will not do the job. I've figured yesterday that I may be able to do a whole bunch of totally amazing things with these paint FX modifiers!
Old 02-08-2014, 11:52 AM   #5
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